Physics of Sound

A waveform is a graph of air pressure over time. The center line is normal air pressure. Above = compression (high pressure). Below = rarefaction (low pressure). This is what you see in your DAW.

One complete wave cycle: starts at zero, rises to peak (maximum compression), returns to zero, drops to trough (maximum rarefaction), returns to zero. The number of cycles per second = frequency in Hertz (Hz).

Western music is based on A4 = 440 Hz (concert pitch). Each octave doubles the frequency. A3 = 220 Hz, A5 = 880 Hz. This exponential relationship is why we perceive octaves as 'the same note, higher/lower.'

The audible spectrum spans roughly 10 octaves (20 Hz to 20 kHz). Different frequency ranges have different characteristics: sub-bass is felt, bass provides foundation, mids carry melody and vocals, highs add air and detail.

Decibels are a logarithmic scale because human hearing is logarithmic. +10 dB ≈ twice as loud (perceived). +6 dB = double the voltage/amplitude. This is why small dB changes matter so much.

dBFS (decibels Full Scale) is the digital meter. 0 dBFS is maximum — above this, digital clipping occurs (harsh distortion). Always leave headroom: aim for peaks around -6 dBFS to -12 dBFS.

When two waves are in phase (aligned), their peaks and troughs add together. The result is a louder combined wave. This is constructive interference — the waves reinforce each other.

When two waves are 180° out of phase (inverted), peaks meet troughs — they cancel each other out. Perfect cancellation results in silence. This is destructive interference — a major mixing concern.

Real-world phase issues are rarely perfect 180° cancellation. Small time delays cause partial phase issues that cancel some frequencies but not others — creating 'comb filtering' (hollow, phasey sound).

Harmonics are integer multiples of the fundamental: 2x, 3x, 4x, etc. The 2nd harmonic (2x) is an octave above. The 3rd (3x) is a fifth + octave. These natural relationships form the basis of musical harmony.

Timbre (tone color) is determined by which harmonics are present and how strong each one is. A flute has mostly fundamental (pure). A violin has rich harmonics (complex). Same note, different character.

Even harmonics (2x, 4x, 6x) are octaves and generally sound musical and warm. Odd harmonics (3x, 5x, 7x) include fifths and can sound edgier. Tube gear adds mostly even harmonics — that's the 'warmth' people describe.

Square waves contain only odd harmonics (3rd, 5th, 7th...), each decreasing in amplitude. Sounds hollow, reedy, like a clarinet or 8-bit video games. Good for bass and lead sounds.

Sawtooth waves contain all harmonics — both odd and even. This makes them the richest, brightest waveform. Sounds buzzy, brassy. The most versatile synth waveform — great for pads, leads, basses.

Triangle waves have odd harmonics like square waves, but they roll off much faster (1/n² vs 1/n). Sounds softer, warmer than square — between sine and square. Good for mellow pads and sub-bass.